Here we focus on the analysis of spiral-tube separators; model selection and the basic parameters for numerical simulation are described. Flow-field simulation analyses were performed for spiral-tube separators both with and without holes. The effects of gyration radius, inlet flowrate, the number of spiral coils, and oil-droplet diameter on flow-field distribution and the separation performance of spiral-tube separators were analysed in detail. The simulation results showed that the gyration radius and inlet velocity are the two main factors affecting the separation characteristics of spiral-tube separators. In addition, the size of the holes in a spiral-tube separator also affects the separation results. Some simulation results were verified through experimental studies. This study provides a basis for the flow-field analysis and structural optimisation of spiral-tube separators. (C) 2011 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.